This invention concerns a method for regulating the supply of weft thread on weaving machines, and also a device which uses this method. In particular, the invention concerns a method and device applicable to weaving machines in which the weft yarn is taken from a yarn supply by means of a yarn draw-off device driven by a motor and consisting of at least one yarn draw-off roller.
A weft preparation mechanism for weft threads is known from French patent application No. 2.508.501, in which use is made of yarn draw-off rollers, an accumulator device and a thread clip for controlling the insertion of the weft thread into the shed. In this mechanism the yarn draw-off rollers are coupled mechanically to the main shaft of the weaving machine. The speed of the yarn draw-off rollers cannot be altered with respect to the speed of the main shaft of the weaving machine. Such a known device has the disadvantage that the insertion thread length cannot be regulated in a simple manner. It is useful to be able to adjust the speed of the yarn draw-off rollers for a number of reasons, for instance to suit the condition and the type of weft yarn supplied. For example, a weft thread drawn from a yarn supply is always under a certain tension, which can vary for various reasons, such as variation in the speed of the thread. Since the yarn draw-off rollers serve to measure off the weft yarn under tension, it is clear that the actual length of the weft yarn released from the yarn draw-off rollers will be smaller than the length measured off. Also, the variations in the tension of the weft yarn as it is drawn off the yarn package cause variations in the thickness of the thread, so that the effective winding diameter of the yarn draw-off rollers is also subject to variation, with the result that variations can also occur in the effective quantity of thread taken from the yarn supply.